Carbon nanotube-graphene hybrid supported platinum as an effective catalyst for hydrogen generation from hydrolysis of ammonia borane

In this study, we report the results of a kinetic study on the hydrogen (H₂) generation from the hydrolysis of ammonia borane (NH₃BH₃) catalyzed by Platinum supported on carbon nanotube-graphene hybrid material (Pt/CNT-G). Synthesized catalyst was characterized by TGA, XRD, CP-OES, TEM and SEM-EDX techniques. Characterization studies have shown that the CNT-G hybrid support material provides desired distribution of the Pt particles on the support material. The effect of various parameters such as catalyst loading, reaction temperature, effect of NaOH and the effect of NH₃BH₃ concentration are also determined. Experimental results showed that the Pt/CNT-G catalyst exhibited high catalytic activity on NH₃BH₃ hydrolysis reaction to release H₂. It has been found that Pt/CNT-G catalyst shows low activation energy of 35.34 kJ mol⁻¹ for hydrolysis reaction of NH₃BH₃. Pt/CNT-G catalyst also exhibited high catalytic activity with turnover frequency (TOF) of 135 (mol_H2/mol_cat.min). Therefore, the synthesized Pt/CNT-G catalyst is a potential candidate for enhanced H₂ generation through NH₃BH₃ hydrolysis.     

Hydrogen generation from the hydrolysis of ammonia-borane using intrazeolite cobalt(0) nanoclusters catalyst

Previously being used as highly active catalyst in the hydrolysis of sodium borohydride, intrazeolite cobalt(0) nanoclusters were also employed as catalyst in the hydrolysis of ammonia-borane (H₃NBH₃). Intrazeolite cobalt(0) nanoclusters were found to be active catalyst in this hydrolysis reaction of ammonia-borane providing 5450 total turnovers at room temperature before deactivation. The results of the kinetic study shows that the catalytic hydrolysis of AB is first order with respect to the catalyst concentration and zero order with respect to substrate concentration. Activation parameters could be obtained from the evaluation of the rate constants at different temperature. The results reveal that intrazeolite cobalt(0) nanoclusters can be considered as promising candidate to be used as catalyst in developing highly efficient portable hydrogen generation systems using ammonia-borane as solid hydrogen storage material.     

Efficient hydrogen production from ammonia borane hydrolysis catalyzed by TiO2-supported RuCo catalysts

Hydrolysis of ammonia borane provides a reliable pathway for hydrogen production, while suitable catalysts are indispensable to make the hydrolysis reaction reach a considerable rate. In the present work, a series of TiO₂-supported RuCo catalysts have been fabricated by coprecipitation and subsequent reduction of Ru³⁺ and Co²⁺ on the surface of TiO₂ nanoparticles. Transmission electron microscopy and elemental mapping have verified the good distribution of metal species in the catalysts. The fabricated catalysts have shown excellent performance for catalyzing ammonia borane hydrolysis, especially in alkaline solutions with 0.5 M NaOH. For Ru₁Co₉/TiO₂ in which Ru/Co molar ratio is 1:9, the active energy of catalyzed ammonia borane hydrolysis is 33.25 kJ/mol, and a turnover frequency based on Ru as high as 1408 mol_H2/(mol_Ru·min) is obtained at 25 °C. Moreover, when different types of TiO₂ substrates are used, anatase TiO₂-supported catalysts show better catalytic activity than their counterparts with rutile TiO₂ as substrate or mixture of anatase and rutile TiO₂ as substrate.     

Co-SiO2 nanosphere-catalyzed hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage

Cobalt clusters-silica nanospheres (15-30 nm) were synthesized using a Co(NH₃)₆Cl₃ template method in a polyoxyethylene-nonylphenyl ether/cyclohexane reversed micelle system followed by in situ reduction in aqueous NaBH₄/NH₃BH₃ solutions. The cobalt clusters are located either inside or on the outer surface of the silica nanospheres as shown by the transmission electron microscope (TEM)/energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements. The cobalt-silica nanospheres have a high catalytic activity for the hydrolysis of ammonia borane that generates a stoichiometric amount of hydrogen, and can be efficiently cycled and reused 10 times without any significant loss of the catalytic activity.     

Ruthenium(0) nanoparticles supported on nanotitania as highly active and reusable catalyst in hydrogen generation from the hydrolysis of ammonia borane

Ruthenium(0) nanoparticles supported on the surface of titania nanospheres (Ru(0)/TiO₂) were in situ generated from the reduction of ruthenium(III) ions impregnated on nanotitania during the hydrolysis of ammonia borane. They were isolated from the reaction solution by centrifugation and characterized by a combination of advanced analytical techniques. The results reveal that highly dispersed ruthenium(0) nanoparticles of size in the range 1.5–3.3 nm were formed on the surface of titania nanospheres. Ru(0)/TiO₂ show high catalytic activity in hydrogen generation from the hydrolysis of ammonia borane with a turnover frequency value up to 241 min⁻¹ at 25.0 ± 0.1 °C. They provide unprecedented catalytic lifetime measured by total turnover number (TTO = 71,500) in hydrogen generation from the hydrolysis of ammonia borane at 25.0 ± 0.1 °C. The report also includes the results of kinetic study on the catalytic hydrolysis of ammonia borane depending on the temperature to determine the activation energy of the reaction (E_a = 70 ± 2 kJ/mol) and the catalyst concentration to establish the rate law of the reaction.     

Rapid preparation of Ru(0) nanoparticles stabilized with water-soluble biopolymer for hydrogen production from ammonia borane: Development of battery-like hydrolysis media

The biohybrid Na-Alg@Ru catalyst was prepared as a result of stabilizing Ru(0) nanoparticles with biopolymer chains of sodium alginate. The in-situ prepared Ru(0) nanoparticles had an average particle size of 1.023 ± 0.097 nm. The monodisperse Ru(0) nanoparticles prepared with a very practical, inexpensive and rapid method were used as a catalyst in hydrogen production by the hydrolysis reaction of ammonia borane (AB). The Na-Alg@Ru catalyst containing 3 mg Ru(0) metal catalyzed the hydrolysis of 50 mM AB with 100% yield, and the activation energy (E_a) of the reaction was estimated as 61.05 kJ mol⁻¹. In addition, the Na-Alg@Ru nanoparticles were prepared with acrylamide as p(AAm)/Na-Alg@Ru hydrogel films suitable for use in hydrogen production in fuel cells, which represents a battery-like environment, and used for hydrogen production from AB. Thus, it was shown that the catalysts prepared in a few nm size could easily be used in battery-like environments.     

CoMoB nanoparticles supported on foam Ni as efficient catalysts for hydrogen generation from hydrolysis of ammonia borane solution

We report on CoMoB nanoparticles supported on foam Ni as catalysts for hydrogen generation from hydrolysis of ammonia borane (NH₃BH₃) solution. The CoMoB/foam Ni catalysts with different molar ratios of Co²⁺and MoO₄²⁻ were synthesized via the electroless-deposition technique at ambient temperature. In order to analyze the phase composition, chemical composition, microstructure, and electron bonding structure of the as-prepared samples, powder X–ray diffraction (XRD), inductively coupled plasma-mass spectroscopy (ICP-MS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used. The results showed that CoMoB nanoparticles were variously dispersed on the surface of the foam Ni and the catalytic activity correlated with the molar ratio of Co²⁺ and MoO₄²⁻. The highest hydrogen generation rate was 5331.0 mL min⁻¹ g_cat⁻¹ at 298 K, and the activation energy was calculated to be 45.5 kJ mol⁻¹ toward the hydrolysis of NH₃BH₃ solution. The better catalytic activity was largely attributed to the smaller particle size, higher surface roughness and the novel three-dimensional cone-like architectures of the obtained samples. The kinetic results show that the hydrolysis of NH₃BH₃ is a first-order reaction in catalyst concentration. In addition, the reusability experiment exhibited that the catalytic activity was reduced after 5 cycles and the reason of the decay was also investigated.     

Catalytic hydrolysis of hydrazine borane for chemical hydrogen storage: Highly efficient and fast hydrogen generation system at room temperature

There has been rapidly growing interest for materials suitable to store hydrogen in solid state for transportation of hydrogen that requires materials with high volumetric and gravimetric storage capacity. B-N compounds such as ammonia-triborane, ammonia-borane and amine-borane adducts are well suited for this purpose due to their light weight, high gravimetric hydrogen storage capacity and inclination for bearing protic (N-H) and hydridic (B-H) hydrogens. In addition to them, more recent study [26] has showed that hydrazine borane with a gravimetric hydrogen storage capacity of 15.4% wt needs to be considered as another B-N compound that can be used for the storage of hydrogen. Herein we report for the first time, metal catalyzed hydrolysis of hydrazine borane (N₂H₄BH₃, HB) under air at room temperature. Among the catalyst systems tested, rhodium(III) chloride was found to provide the highest catalytic activity in this reaction. In the presence of rhodium(III) chloride, the aqueous solution of hydrazine borane undergoes fast hydrolysis to release nearly 3.0 equivalent of H₂ at room temperature with previously unprecedented H₂ generation rate TOF = 12000 h⁻¹. More importantly, it was found that in the catalytic hydrolysis of hydrazine borane the reaction between hydrazine borane and water proceeds almost in stoichiometric proportion indicating that the efficient hydrogen generation can be achieved even from the highly concentrated solution of hydrazine borane or in the solid state when water added to the solid hydrazine borane. This finding is crucial especially for on-board application of the existing system. The work reported here also includes (i) finding the solubility of hydrazine borane plus its stability against self-hydrolysis in water, (ii) the definition of reaction stoichiometry and the identification of reaction products for the catalytic hydrolysis of hydrazine borane, (iii) the collection of wealthy kinetic data to demonstrate the effect of substrate and catalyst concentrations on the hydrogen generation rate and to determine the rate law for the catalytic hydrolysis of hydrazine borane, (iv) the investigation of the effect of temperature on the rate of hydrogen generation and determination of activation parameters (E_a, ΔH^#, and ΔS^#) for the catalytic hydrolysis of hydrazine borane.     

Hydroxyapatite-supported palladium(0) nanoclusters as effective and reusable catalyst for hydrogen generation from the hydrolysis of ammonia-borane

Herein we report the preparation, characterization and catalytic use of hydroxyapatite-supported palladium(0) nanoclusters in the hydrolysis of ammonia-borane. Palladium(0) nanoclusters were formed in situ from the reduction of palladium(II) ion exchanged hydroxyapatite during the hydrolysis of ammonia-borane and supported on hydroxyapatite. The hydroxyapatite-supported palladium(0) nanoclusters are stable enough to be isolated as solid materials and characterized by using a combination of advanced analytical techniques. They are isolable, redispersible and reusable as an active catalyst in the hydrolysis of ammonia-borane even at low concentration and temperature. They provide a maximum hydrogen generation rate of ∼1425 mL H₂ min⁻¹ (g Pd)⁻¹ and 12300 turnovers in the hydrolysis of ammonia-borane at 25 ± 0.1 °C before deactivation. The work reported here also includes the full experimental details for the collection of a wealth of kinetic data to determine the activation energy (E_a = 54.8 ± 2.2 kJ/mol) and the effect of catalyst concentration on the rate for the catalytic hydrolysis of ammonia-borane.     

Water soluble nickel(0) and cobalt(0) nanoclusters stabilized by poly(4-styrenesulfonic acid-co-maleic acid): Highly active, durable and cost effective catalysts in hydrogen generation from the hydrolysis of ammonia borane

This paper reports the in-situ generation and catalytic activity of nickel(0) and cobalt(0) nanoclusters stabilized by poly(4-styrene sulfonic acid-co-maleic acid), PSSA-co-MA, in the hydrolysis of ammonia borane (AB). PSSA-co-MA stabilized nickel(0) (PSMA-Ni) and cobalt(0) nanoclusters (PSMA-Co) having average particle size of 2.1 ± 0.6 and 5.3 ± 1.6 nm, respectively, were generated by in-situ reduction of nickel(II) chloride or cobalt(II) chloride in an aquoues solution of NaBH₄/H₃NBH₃ in the presence of PSSA-co-MA. The in-situ generated nanoclusters were isolated from the reaction solution and characterized by UV-Vis, TEM, XRD and FT-IR techniques. Compared with the previous catalyst systems, PSMA-Ni and PSMA-Co are found to be highly active catalysts for hydrogen generation from the hydrolysis of AB with the turnover frequency values of 10.1 min⁻¹ for Ni and 25.7 min⁻¹ for Co. They are also very stable during the hydrolysis of AB providing 22450 and 17650 turnovers, respectively. The results of mercury poisoning experiments reveal that PSMA-Ni and PSMA-Co are heterogeneous catalysts in the hydrolysis of AB. Herein, we also report the results of a detailed kinetic study on the hydrogen generation from the hydrolysis of AB catalyzed by PSMA-Ni and PSMA-Co depending on catalyst concentration, substrate concentration, and temperature along with the activation parameters of catalytic hydrolysis of AB calculated from the kinetic data.     

A highly efficient Co (0) catalyst derived from metal-organic framework for the hydrolysis of ammonia borane

A Co (0) catalyst is synthesized by the reduction of a metal-organic framework (MOF) precursor Co₂(bdc)₂(dabco) (bdc = 1,4-benzenedicarboxylate; dabco = 1,4-diazabicyclo[2.2.2]octane). The amorphous catalyst exhibits highly efficient activity in the hydrolysis of ammonia borane (AB). The dehydrogenation of a 0.32 M aqueous AB solution completes in 1.4 min under room temperature. The porous structure in the MOF is proposed to play a key role. The catalytic effective Co (0) sites are stabilized by the organic molecules, which used to coordinate to Co (II) in the MOF precursor. This work implies that MOFs, with their large surface area and ample pore structures, may serve as ideal precursors for highly efficient heterogeneous catalysts.     

Hydrogen generation by hydrolysis of ammonia borane with a nanoporous cobalt-tungsten-boron-phosphorus catalyst supported on Ni foam

In this study, quaternary cobalt-tungsten-boron-phosphorus porous particles supported on Ni foam (Co-W-B-P/Ni), which are prepared through ultrasonification-assisted electroless deposition route, have been investigated as the catalyst for hydrogen generation (HG) from hydrolysis of ammonia borane (NH₃BH₃, AB). Compared with Ni-supported binary Co-B and ternary Co-W-B catalysts, the as-synthesized Co-W-B-P/Ni shows a higher HG rate. To optimize the preparation parameters, the molar ratio of NaBH₄/NaH₂PO₂·H₂O (B/P) and the concentration of Na₂WO₄·2H₂O (W) have been investigated and the catalyst prepared with B/P value of 1.5 and W concentration of 5 g L⁻¹ shows the highest activity. The results of kinetic studies show that the catalytic hydrolysis of AB is first order with respect to the catalyst and AB concentrations. By using the quaternary catalyst with a concentration of 0.5 wt % AB, a HG rate of 4.0 L min⁻¹ g⁻¹ is achieved at 30 °C. Moreover, the apparent activation energy for the quaternary catalyst is determined to be 29.0 kJ mol⁻¹, which is comparable to that of noble metal-based catalysts. These results indicate that the Co-W-B-P/Ni is a promising low-cost catalyst for on-board hydrogen generation from hydrolysis of borohydride.     

Zeolite confined palladium(0) nanoclusters as effective and reusable catalyst for hydrogen generation from the hydrolysis of ammonia-borane

Zeolite confined palladium(0) nanoclusters were prepared by a two step procedure: incorporation of Pd²⁺ ions into the zeolite-Y by ion-exchange followed by the reduction of Pd²⁺ ions in the supercages of zeolite-Y with sodium borohydride at room temperature. Zeolite confined palladium(0) nanoclusters are stable enough to be isolated as solid materials and characterized by ICP-OES, XRD, HRTEM, SEM, X-ray photoelectron spectroscopy and N₂ adsorption technique. These nanoclusters are isolable, redispersible and reusable as an active catalyst in the hydrolysis of ammonia-borane solution. Zeolite confined palladium(0) nanoclusters provide 15,600 turnovers in hydrogen generation from the hydrolysis of ammonia-borane at 25.0 ± 0.1 °C.     

Nanoporous Ni-based catalysts for hydrogen generation from hydrolysis of ammonia borane

We report nanoporous Ni, Ni–Fe, and Ni–Pt as catalysts for hydrogen generation from hydrolytic dehydrogenation of ammonia borane (NH₃BH₃, AB). The Ni and Ni–Fe nanoparticles with diameters of 20–25 nm were synthesized by a colloidal method in starch-containing aqueous solution. They exhibited considerable in situ catalytic performance but severely lost activity after separating from the reaction solution. Nanoporous Ni_1−xPt_x (x = 0.01, 0.08 and 0.19) with particle size below 5 nm was prepared from the isolated Ni nanoparticles through a replacement reaction. After centrifugation, drying, washing, and annealing, the obtained nanoporous Ni–Pt could attain remarkable activity, high hydrogen generation rate and efficiency, and low activation energy.     

Coupling ultralow-content ruthenium with nickel hydroxide via corrosion engineering for highly efficient hydrogen generation from ammonia borane

Efficient and controllable release of hydrogen from solid hydrogen storage materials is a promising way to produce hydrogen safely and on-demand. The development of economical, highly active, easily recyclable catalysts is critical for practical applications, which remains a great challenging. Herein, the easily controllable and cost-effective corrosion strategy is ingeniously developed to simply prepare ultralow-content ruthenium coupled with nickel hydroxide on nickel foam (Ru–Ni–NF). After experiencing the spontaneous oxidation-reduction reactions between the reactive NF and Ru³⁺, ultrafine Ru nanoparticles decorated nickel hydroxide nanosheets are in situ intimately grown on porous NF networks. The optimal Ru–Ni–NF catalyst exhibits the excellent performance for catalytic hydrolysis of ammonia borane with a high turnover frequency (TOF) of 539.6 mol_H2 mol_Ru^?1 min^?1 at 298 K and a low apparent activation energy of 36.4 kJ mol^?1, due to the synergistic effect between Ru nanoparticles and nickel hydroxide nanosheets. Furthermore, the Ru–Ni–NF catalyst possesses easy separation and outstanding durability, which is superior to powdered catalysts. This study provides a facile and economical strategy for the preparation of ultralow-content noble metal supported metal foam-type catalysts for dehydrogenation of ammonia borane.     

Low-cost CuFeCo@MIL-101 as an efficient catalyst for catalytic hydrolysis of ammonia borane

Trimetallic nanoparticles of non-noble Cu–Fe–Co with different molar ratios were successfully immobilized in the metal-organic frameworks (MIL-101) via an easy impregnation–reduction process. XRD, TEM, XPS, ICP-MS and BET methods were used to characterize the catalyst. Comparing to their bimetallic counterparts, Cu₆Fe_0.8Co_3.2@MIL-101 demonstrates the best catalytic performance for dehydrogenation of ammonia borane by hydrolysis at 298 K Cu₆Fe_0.8Co_3.2@MIL-101 shows a total turnover frequency (TOF) value of 23.2 mol_H2 mol_catalyst⁻¹ min⁻¹ and an activation energy value of 37.1 kJ mol⁻¹. The enhancement of catalytic activity was attributed to a synergistic effect among copper, cobalt and iron nanoparticles supported on MIL-101. In addition, the catalyst still exhibits good stability and magnetic recyclability after seven cycles. The low-cost catalyst has good prospect for application in the field of hydrogen storage.     

A highly active Co-B catalyst for hydrogen generation from sodium borohydride hydrolysis

Co-B catalysts were prepared by the chemical reduction of CoCl₂ with NaBH₄ for hydrogen generation from borohydride hydrolysis. The catalytic properties of the Co-B catalysts were found to be sensitive to the preparation conditions including pH of the NaBH₄ solution and mixing manner of the precursors. A Co-B catalyst with a very high catalytic activity was obtained through the formation of a colloidal Co(OH)₂ intermediate. The ultra-fine particle size of 10 nm accounted for its super activity for hydrogen generation with a maximum rate of 26 L min⁻¹ g⁻¹ at 30 °C. The catalyst also changed the hydrolysis kinetics from zero-order to first-order.     

Hydrogen production from hydrolysis of ammonia borane with limited water supply

Effect of limited water supply to hydrolysis of ammonia borane for hydrogen evolution is studied over the cases in which the initial molar ratio of water to ammonia borane (H₂O/AB) is set at 1.28, 2.57 and 4.50. The conversion efficiency of ammonia borane to hydrogen is estimated from the accumulated volume of produced hydrogen gas and the quantitative analysis of hydrolysate by solid-state ¹¹B NMR. Characteristics of hydrogen evolution are significantly influenced by both water dosage and injection rate of water. In the case that water is a limiting agent, namely, H₂O/AB = 1.28, less hydrogen is produced than that predicted stoichiometrically. In contrast, conversion efficiency of ammonia borane reaches nearly 100% for the case with H₂O/AB = 4.50. Injection rate of water to ammonia borane also affect profoundly the produced volume and production rate of hydrogen, if water is used as a limiting agent in the hydrolysis of ammonia borane. Nonetheless, boric acid and metaboric acid are found to be the dominant products in the hydrolysate from XRD, FT-IR and solid-state ¹¹B NMR analysis. The hydrogen storage capacity using limited water supply in this work could reach as high as about 5.33 wt%, based on combined mass of reactants and catalyst.     

Noble-metal-free Co@Co2P/N-doped carbon nanotube polyhedron as an efficient catalyst for hydrogen generation from ammonia borane

Developing an efficient catalyst for hydrogen (H₂) generation from hydrolysis of ammonia borane (AB) to significantly improve the activity for the hydrogen generation from AB is important for its practical application. Herein, we report a novel hybrid nanostructure composed of uniformly dispersed Co@Co₂P core-shell nanoparticles (NPs) embedded in N-doped carbon nanotube polyhedron (Co@Co₂P/N–CNP) through a carbonization-phosphidation strategy derived from ZIF-67. Benefiting from the electronic effect of P doping, high dispersibility and strong interfacial interaction between Co@Co₂P and N-CNTs, the Co@Co₂P/N–CNP catalyst exhibits excellent catalytic performance towards the hydrolysis of AB for hydrogen generation, affording a high TOF value of 18.4 mol H₂ mol metal^?1 min^?1 at the first cycle. This work provides a promising lead for the design of efficient heterogeneous catalysts towards convenient H₂ generation from hydrogen-rich substrates in the close future.